mirror of
https://github.com/hsoft/collapseos.git
synced 2024-11-01 17:30:55 +11:00
299 lines
6.1 KiB
NASM
299 lines
6.1 KiB
NASM
; vdp - console on SMS' VDP
|
|
;
|
|
; Implement PutC on the console. Characters start at the top left. Every PutC
|
|
; call converts the ASCII char received to its internal font, then put that
|
|
; char on screen, advancing the cursor by one. When reaching the end of the
|
|
; line (33rd char), wrap to the next.
|
|
;
|
|
; In the future, there's going to be a scrolling mechanism when we reach the
|
|
; bottom of the screen, but for now, when the end of the screen is reached, we
|
|
; wrap up to the top.
|
|
;
|
|
; When reaching a new line, we clear that line and the next to help readability.
|
|
;
|
|
; *** Defines ***
|
|
; FNT_DATA: Pointer to 7x7 font data.
|
|
; *** Consts ***
|
|
;
|
|
.equ VDP_CTLPORT 0xbf
|
|
.equ VDP_DATAPORT 0xbe
|
|
|
|
; *** Variables ***
|
|
;
|
|
; Row of cursor
|
|
.equ VDP_ROW VDP_RAMSTART
|
|
; Line of cursor
|
|
.equ VDP_LINE @+1
|
|
.equ VDP_RAMEND @+1
|
|
|
|
; *** Code ***
|
|
|
|
vdpInit:
|
|
xor a
|
|
ld (VDP_ROW), a
|
|
ld (VDP_LINE), a
|
|
|
|
ld hl, vdpInitData
|
|
ld b, vdpInitDataEnd-vdpInitData
|
|
ld c, VDP_CTLPORT
|
|
otir
|
|
|
|
; Blank VRAM
|
|
xor a
|
|
out (VDP_CTLPORT), a
|
|
ld a, 0x40
|
|
out (VDP_CTLPORT), a
|
|
ld bc, 0x4000
|
|
.loop1:
|
|
xor a
|
|
out (VDP_DATAPORT), a
|
|
dec bc
|
|
ld a, b
|
|
or c
|
|
jr nz, .loop1
|
|
|
|
; Set palettes
|
|
xor a
|
|
out (VDP_CTLPORT), a
|
|
ld a, 0xc0
|
|
out (VDP_CTLPORT), a
|
|
xor a ; palette 0: black
|
|
out (VDP_DATAPORT), a
|
|
ld a, 0x3f ; palette 1: white
|
|
out (VDP_DATAPORT), a
|
|
|
|
; Define tiles
|
|
xor a
|
|
out (VDP_CTLPORT), a
|
|
ld a, 0x40
|
|
out (VDP_CTLPORT), a
|
|
ld hl, FNT_DATA
|
|
ld c, 0x7e-0x20 ; range of displayable chars in font.
|
|
; Each row in FNT_DATA is a row of the glyph and there is 7 of them.
|
|
; We insert a blank one at the end of those 7. For each row we set, we
|
|
; need to send 3 zero-bytes because each pixel in the tile is actually
|
|
; 4 bits because it can select among 16 palettes. We use only 2 of them,
|
|
; which is why those bytes always stay zero.
|
|
.loop2:
|
|
ld b, 7
|
|
.loop3:
|
|
ld a, (hl)
|
|
out (VDP_DATAPORT), a
|
|
; send 3 blanks
|
|
xor a
|
|
out (VDP_DATAPORT), a
|
|
nop ; the VDP needs 16 T-states to breathe
|
|
out (VDP_DATAPORT), a
|
|
nop
|
|
out (VDP_DATAPORT), a
|
|
inc hl
|
|
djnz .loop3
|
|
; Send a blank row after the 7th row
|
|
xor a
|
|
out (VDP_DATAPORT), a
|
|
nop
|
|
out (VDP_DATAPORT), a
|
|
nop
|
|
out (VDP_DATAPORT), a
|
|
nop
|
|
out (VDP_DATAPORT), a
|
|
dec c
|
|
jr nz, .loop2
|
|
|
|
; Bit 7 = ?, Bit 6 = display enabled
|
|
ld a, 0b11000000
|
|
out (VDP_CTLPORT), a
|
|
ld a, 0x81
|
|
out (VDP_CTLPORT), a
|
|
ret
|
|
|
|
; Spits char set in A at current cursor position. Doesn't move the cursor.
|
|
; A is a "sega" char
|
|
vdpSpitC:
|
|
; store A away
|
|
ex af, af'
|
|
push bc
|
|
ld b, 0 ; we push rotated bits from VDP_LINE into B so
|
|
; that we'll already have our low bits from the
|
|
; second byte we'll send right after.
|
|
; Here, we're fitting a 5-bit line, and a 5-bit column on 16-bit, right
|
|
; aligned. On top of that, our righmost bit is taken because our target
|
|
; cell is 2-bytes wide and our final number is a VRAM address.
|
|
ld a, (VDP_LINE)
|
|
sla a ; should always push 0, so no pushing in B
|
|
sla a ; same
|
|
sla a ; same
|
|
sla a \ rl b
|
|
sla a \ rl b
|
|
sla a \ rl b
|
|
ld c, a
|
|
ld a, (VDP_ROW)
|
|
sla a ; A * 2
|
|
or c ; bring in two low bits from VDP_LINE into high
|
|
; two bits
|
|
out (VDP_CTLPORT), a
|
|
ld a, b ; 3 low bits set
|
|
or 0x78 ; 01 header + 0x3800
|
|
out (VDP_CTLPORT), a
|
|
pop bc
|
|
|
|
; We're ready to send our data now. Let's go
|
|
ex af, af'
|
|
out (VDP_DATAPORT), a
|
|
ret
|
|
|
|
vdpPutC:
|
|
; Then, let's place our cursor. We need to first send our LSB, whose
|
|
; 6 low bits contain our row*2 (each tile is 2 bytes wide) and high
|
|
; 2 bits are the two low bits of our line
|
|
; special case: line feed, carriage return, back space
|
|
cp LF
|
|
jr z, vdpLF
|
|
cp CR
|
|
jr z, vdpCR
|
|
cp BS
|
|
jr z, vdpBS
|
|
|
|
push af
|
|
|
|
; ... but first, let's convert it.
|
|
call vdpConv
|
|
|
|
; and spit it on screen
|
|
call vdpSpitC
|
|
|
|
; Move cursor. The screen is 32x24
|
|
ld a, (VDP_ROW)
|
|
cp 31
|
|
jr z, .incline
|
|
; We just need to increase row
|
|
inc a
|
|
ld (VDP_ROW), a
|
|
|
|
pop af
|
|
ret
|
|
.incline:
|
|
; increase line and start anew
|
|
call vdpCR
|
|
call vdpLF
|
|
pop af
|
|
ret
|
|
|
|
vdpCR:
|
|
call vdpClrPos
|
|
push af
|
|
xor a
|
|
ld (VDP_ROW), a
|
|
pop af
|
|
ret
|
|
|
|
vdpLF:
|
|
; we don't call vdpClrPos on LF because we expect it to be preceded by
|
|
; a CR, which already cleared the pos. If we cleared it now, we would
|
|
; clear the first char of the line.
|
|
push af
|
|
ld a, (VDP_LINE)
|
|
call .incA
|
|
call vdpClrLine
|
|
; Also clear the line after this one
|
|
push af ; --> lvl 1
|
|
call .incA
|
|
call vdpClrLine
|
|
pop af ; <-- lvl 1
|
|
ld (VDP_LINE), a
|
|
pop af
|
|
ret
|
|
.incA:
|
|
inc a
|
|
cp 24
|
|
ret nz ; no rollover
|
|
; bottom reached, roll over to top of screen
|
|
xor a
|
|
ret
|
|
|
|
vdpBS:
|
|
call vdpClrPos
|
|
push af
|
|
ld a, (VDP_ROW)
|
|
or a
|
|
jr z, .lineup
|
|
dec a
|
|
ld (VDP_ROW), a
|
|
pop af
|
|
ret
|
|
.lineup:
|
|
; end of line
|
|
ld a, 31
|
|
ld (VDP_ROW), a
|
|
; we have to go one line up
|
|
ld a, (VDP_LINE)
|
|
or a
|
|
jr z, .nowrap
|
|
; We have to wrap to the bottom of the screen
|
|
ld a, 24
|
|
.nowrap:
|
|
dec a
|
|
ld (VDP_LINE), a
|
|
pop af
|
|
ret
|
|
|
|
; Clear tile under cursor
|
|
vdpClrPos:
|
|
push af
|
|
xor a ; space
|
|
call vdpSpitC
|
|
pop af
|
|
ret
|
|
|
|
; Clear line number A
|
|
vdpClrLine:
|
|
; see comments in vdpSpitC for VRAM details.
|
|
push af
|
|
; first, get the two LSB at MSB pos.
|
|
rrca \ rrca
|
|
push af ; --> lvl 1
|
|
and 0b11000000
|
|
; That's our first address byte
|
|
out (VDP_CTLPORT), a
|
|
pop af ; <-- lvl 1
|
|
; Then, get those 3 other bits at LSB pos. Our popped A has already
|
|
; done 2 RRCA, which means that everything is in place.
|
|
and 0b00000111
|
|
or 0x78
|
|
out (VDP_CTLPORT), a
|
|
; We're at the right place. Let's just spit 32*2 null bytes
|
|
xor a
|
|
push bc ; --> lvl 1
|
|
ld b, 64
|
|
.loop:
|
|
out (VDP_DATAPORT), a
|
|
djnz .loop
|
|
pop bc ; <-- lvl 1
|
|
pop af
|
|
ret
|
|
|
|
; Convert ASCII char in A into a tile index corresponding to that character.
|
|
; When a character is unknown, returns 0x5e (a '~' char).
|
|
vdpConv:
|
|
; The font is organized to closely match ASCII, so this is rather easy.
|
|
; We simply subtract 0x20 from incoming A
|
|
sub 0x20
|
|
cp 0x5f
|
|
ret c ; A < 0x5f, good
|
|
ld a, 0x5e
|
|
ret
|
|
|
|
; VDP initialisation data
|
|
vdpInitData:
|
|
; 0x8x == set register X
|
|
.db 0b00000100, 0x80 ; Bit 2: Select mode 4
|
|
.db 0b00000000, 0x81
|
|
.db 0b11111111, 0x82 ; Name table: 0x3800
|
|
.db 0b11111111, 0x85 ; Sprite table: 0x3f00
|
|
.db 0b11111111, 0x86 ; sprite use tiles from 0x2000
|
|
.db 0b11111111, 0x87 ; Border uses palette 0xf
|
|
.db 0b00000000, 0x88 ; BG X scroll
|
|
.db 0b00000000, 0x89 ; BG Y scroll
|
|
.db 0b11111111, 0x8a ; Line counter (why have this?)
|
|
vdpInitDataEnd:
|